1. Field of the Invention
The present invention relates to an adhesive composition, and in particular to a water soluble adhesive composition having superior water resistance and water retention.
2. Background of the Invention
water soluble adhesives used in the manufacture of pressure sensitive adhesive tapes normally contain water glue, dextrin or polyvinyl alcohol, and are usually applied to paper tapes to form adhesive tapes for use. When this kind of adhesive tapes are dried, they lose their rubber elasticity and viscosity, and consequently lose their pressure sensitive adhesive performance. Complicated apparatuses for imparting moisture to the surface of this kind of adhesive tapes prior to use are then required to recover the adhesive strength thereof.
Other water soluble:adhesives suitable for use in pressure sensitive adhesive tapes, for example those containing polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl methyl ether, or copolymer of maleic anhydride and vinyl methyl ether as raw material exhibit bad water resistance and cohesion, and can not be preserved at high temperature or high humidity. If the adhesives are preserved for a prolonged period, the adhesives flow out and leak out due to the absorption of moisture, thereby causing a slippage of the adhesive tapes from the material or article to which they adhere. In order to obtain sufficient adhesive strength under low temperature and humidity, a large amount of low molecular water soluble modifiers are required to compound in the adhesives. The modified adhesives, however, when being used at an elevated temperature, will cause migration, making the adhering-surfaces move and thus diminishing the adhesive strength thereof.
Hydrophobic adhesives, that is, oil soluble adhesives, for example, those produced by using natural rubber or synthetic rubbers such as polyisoprene, polybutene, and polyisobutylene; acrylic resins such as ethylacrylate, 2-ethylhexyl acrylate, and isoctyl acrylate; and silicon polymers such as polydimethyl siloxane, polysilicate resin siloxane blends as raw materials, exhibit an enhanced adhesive strength, yet when the surface of the object to be adhered is wet, the adhesive strength is noticably reduced. And when the hydrophobic adhesive tapes are torn from the object they adhered, residues remain thereon and are not easy to remove. Also, the hydrophobic adhesives irritate human skin and are therfore not suitable for use with surgical tapes.
In addition, all of the above mentioned conventional adhesives do not show good water retention, and therefore when they are dried, their adhesive properties are reduced.